Carbapenem-resistant Enterobacteriaceae (CRE) represent an immediate public health threat that requires urgent and aggressive action. To date, most CRE infections are healthcare associated (HA). However, the molecular epidemiology of other multidrug resistant organisms (MDRO) such as methicillin-resistant Staphylococcus aureus (MRSA) and Clostridium difficile suggests that progression to community-associated (CA) CRE is an imminent threat. Early recognition of potential CA-CRE strains and a clear biological understanding of mechanisms resulting in community transmission is essential for an appropriate response. The Consortium on Resistance against Carbapenems in Klebsiella and other Enterobacteriaceae (CRACKLE) is a prospective, international, multicenter, observational ongoing study for which Dr. van Duin is the PI. CRACKLE is federally funded through and data-shares with the Antibacterial Resistance Leadership Group (ARLG). In CRACKLE, all patients at participating hospitals who have CRE isolated from a clinical culture during hospitalization are included. Our preliminary data from CRACKLE indicate an increase in the US in possible CA-CRE infections. Our overall hypothesis is that enhanced intestinal colonization is a final common pathway for community spread of CRE strains that are responsible for increasing CA-CRE infections in the US. Enhanced ability to establish intestinal colonization, especially in the absence of antimicrobial-induced dysbiosis is proposed to be a prerequisite for successful community spread of CRE. In line with this hypothesis, our preliminary data shows a relative lack of fimE in CRE from patients admitted from home without obvious healthcare exposures. Absence of fimE results in over-expression of type 1 fimbriae, which are known to be involved in intestinal colonization. In this proposal, we will use CRACKLE infrastructure to evaluate current CA-CRE infections in the US and study CRE spread in the community (Aim 1). The intestinal colonization potential of various CRE strains will be determined in human intestinal cell adhesion and murine intestinal colonization assays with increasing antibiotic pressures (Aim 2). Finally, we will determine which bacterial chromosomal and/or plasmid genetic characteristics are associated with the CA-CRE phenotype, by performing whole genome analysis and plasmid analysis (Aim 3). This genetic analysis will focus on gene families that are known to play a role in intestinal colonization such as fim. Together, these studies will allow for early discovery of CRE strains and/or carbapenemase gene-carrying plasmids with potential for community spread resulting in guided efforts to prevent widespread community dissemination of CRE.